Ferritic alloys



United States Patent FERRITIC ALLOYS Henry William Kirkby and CharlesSykes, Sheflield, England, assignors, by mesne assignments, toFirth-Vickers Stainless Steels Limited, Shellield, England, a Britishcompany No Drawing. Application April 1, 1953, Serial No. 346,257

Claims priority, application Great Britain May 28, 1952 3 Claims. (Cl.75-128) This invention relates to ferritic alloys and is concerned withthe provision of forgeable high strength ferritic alloys possessing agood combination of strength and duetility coupled with stainless and(if required) non-scaling properties, without having recourse to theusual hardening and tempering processes.

Normally, high strength structural steels owe their characteristicphysical properties to the peculiar relationship between the carbon andiron contents, which, in some cases, may be implemented by suitablealloying elements. With these steels, it is necessary for attainment ofthe deirable properties to submit them to thermal treatments comprisingheating into the gamma (or austenitic) region, cooling at not less thana certain rate (e. g. air, oil or water cooled) followed by a temperingor letting down process to the required strength. Failure to use theappropriate hardening temperatures and cooling rates often leads to thematerial being too high in strength and low in ductility or vice versa.

A further difficulty in regard to the type of steel in question, is thatwhere high chromium contents are used to impart rustless andscale-resisting properties it is necessary to use relatively higherhardening temperatures with consequent greater risks of warpage, loss ofmetal and/or spoiling of the surface appearance. This latter diflicultyhas a particular bearing in those cases where the article is required tomeet close dimensional requirements such as with precision stampedarticles.

This invention provides a ferritic alloy which does not rely on theelement carbon and associated thermal treatments to impart the necessarystrength, but upon the use of a selected critical balance of alloyingelements with iron, which elements (each present within a criticalrange) collectively have a natural intrinsic hardness and strength.

The alloys according to the invention comprise the following range ofcomposition:

Carbon Up to 0.1%.

Silicon 1.5 to 6.0%.

Manganese 0.5 to 5.0%.

Nickel 0.5 to 6.0%.

Chromium 3.0 to 16.0%.

Iron The substantial remainder.

Niobium, titanium, vanadium or molybdenum, either singly or incombination, may be present in small quantities up to a total maximum of1.0%

The preferred range is:

Carbon 0.1% maximum. Silicon 2.0 to 5.0%. Manganese 2.0 to 4.0%. Nickel3.0 to 6.0%. Chromium 8.0 to 14.0%. Titanium or niobium Up to 0.75%.Iron Remainder.

The following are examples of alloys embodying the invention and oftheir typical properties:

ice

Composition 0, Si, Mn, Ni, Or, 'li, Nb, Per Per- Per- Per- Per- Per-Percent cent cent cent cent cent cent Alloy 1L. 2. 50 3. 59 13. 64 .l 0.52 Alloy B 3. 14 5. 16 8. 50 Alloy C 3. 22 5. 25 8. 57 0. 37

Properties $5 2 535. s tlfii i Izod tons per tons pe r g area, a sq.inch sq. inch p we percent 5 Alloy A 49. 0 65. 0 24 56 77 Alloy B 62. 084. 5 20 47 Alloy C 54. 8 83.0 21. 5 41 The alloys of the invention are,for all practical purposes, unaffected by thermal treatments andconsequently do not require hardening and tempering as is the case withthe normal high srength ferritic alloys previously referred to. Where,however, cold work has been applied during fabrication, it may benecessary to employ a stress-relieving treatment, carried out at, say,650-700 C. The following results of tests, carried out on alloys of thecomposition A referred to above, illustrate the non-sensitivity to heattreatment of the alloys of the present invention:

We claim:

1. A forgeable high strength fem'tic alloy comprising carbon up to 0.1%,silicon 1.5 to 6.0%, manganese 0.5 to 5.0%, nickel 0.5 to 6.0%, chromium3.0 to 16.0%, and the balance iron with residual impurities in ordinaryamounts.

2. A forgeable high strength ferritis alloy comprising carbon up to0.1%, silicon 1.5 to 6.0%, manganese 0.5 to 5.0%, nickel 0.5 to 6.0%,chromium 3.0 to 16.0%, up to 1.0% of an alloying constituent consistingof at least one metal selected from a group consisting of niobium,titanium, vanadium, molybdenum and the balance iron with residualimpurities in ordinary amounts 3. A forgeable high strength ferriticalloy comprising carbon up to 1.0%, silicon 2.9 to 5.0%, manganese 2.0to 4.0%, nickel 3.0 to 6.0%, chromium 8.0 to 14.0%, up to 0.75% of ametal selected from the group consisting of titanium and niobium, andthe balance iron with residual impurities in ordinary amounts ReferencesCited in the file of this patent UNITED STATES PATENTS 2,225,730Armstrong Dec. 24, 1940 FOREIGN PATENTS 625,055 France Aug. 2, 1927897,766 France Mar. 30, 1945

1. A FORGEABLE HIGH STRENGTH FERRITIC ALLOY COMPRISING CARBON UP TO0.1%, SILICON 1.5 TO 6.0%, MANAGANESE 0.5 TO 5.0%, NICKEL 0.5 TO 6.0%,CHROMIUM 3.0 TO 16.0%, AND THE BALANCE IRON WITH RESIDUAL IMPURITIES INORDINARY AMOUNTS.